Brian
Don't think you are correct on this. As I understand it, RS-422 is differential, i.e. it uses two lines (for TX and 2 for RX)and the difference between them is the signal. RS-232 uses 1 line TX and 1 for RX with a common ground. The signal is between the line and the ground. Most RS-232 receivers on PCs can handle using one side of the RS-422 just fine. RS-422 is more robust when it comes to noise. NMEA 0183 is based on RS-422 electrical specs.

Paul L